TITLE: GCN CIRCULAR NUMBER: 23979 SUBJECT: GRB190320A: MASTER GRB counterpart decay DATE: 19/03/20 09:06:20 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, E. Gorbovskoy, N.Tyurina, V.Kornilov, D.Vlasenko, V.Vladimirov, D.Zimnukhov, A.Kuznetsov, P.Balanutsa, A. Chasovnikov, V.Topolev, D.Kuvshinov (Lomonosov Moscow State University, SAI, Physics Department), R. Podesta, C. Lopez, C.Francile, F. Podesta (Observatorio Astronomico Felix Aguilar OAFA, San Juan National University), H.Levato (Instituto de Ciencias Astronomicas, de la Tierra y del Espacio ICATE, SJNU) R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres (The Instituto de Astrofisica de Canarias), D. Buckley (South African Astronomical Observatory), O. Gress, N.M. Budnev, O.Ershova, Yu.Ishmuhametova, S.Yazev (Applied Physics Institute, Irkutsk State University), V. Yurkov, A. Gabovich, Yu. Sergienko, D. Kobcev (Blagoveschensk Educational State University), A. Tlatov, V.Senik, A.V. Parhomenko, D. Dormidontov (Kislovodsk Solar Stationof the Pulkovo Observatory), MASTER-OAFA robotic telescope (Global MASTER-Net http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy,vol. 2010, 30L) located in Argentina (OAFA observatory of San JuanNational University) was pointed to the Swift GRB190320A (Kennea et al. GCN 23974, Gropp et al. GCN 23973, Lipunov et al. GCN 23975) 21 sec after notice time (82 sec after trigger time) at 2019-03-20 01:15:58 UT (Lipunov et al. GCN 23975) MASTER-OAFA find a new object MASTER OT J075123.56-455316.54 (Lipunov et al. GCN 23976) within Swift GRB 190320A error box (Kennea et al. GCN 23976, Osborne et al. GCN23977) at position RA,Dec(2000)=07h 51m 23.56s , -45d 53m 16.54s (+-0.7") MASTER OT J075123.56-455316.54 decay by 1 magnitude during several minutes. The reduction is continued.